Computerized scintigraphy employing the gamma camera will be used to study the dynamics of the pulmonary capillary membrane leak of 99m technetium human serum albumin (Tc-HSA) in the acute respiratory distress syndrome (ARDS). In preliminary canine studies, the severity of oleic acid-induced albumin leak was proportional to the slope of a rising lung: heart radioactivity ratio and was more sensitive than arterial blood gases and standard chest roentgenograms. We have called this rising ratio the "slope index" (SI). Altered pulmonary vascular recruitment following left atrial balloon inflation or opening a large aorto-inferior vena caval shunt, did not produce a rising radioactivity ratio following equilibration. However, once oleic acid injury was created, increased pulmonary vascular recruitment increased the rate of scintigraphically measured albumin flux. The method is noninvasive and can be used clinically to determine the severity and duration of non-cardiogenic pulmonary edema. Thirty-five scintigraphic studies have been obtained in 29 patients. A positive study was associated with impaired gas exchange as measured by a significantly lower (a/A)O2 ratio when ventilated with a significantly higher amount of PEEP than those patients with negative scintigraphic studies. Positive SI's were noted between 24 hours and 8 days after the clinical onset of ARDS and returned to normal in four patients following clinical resolution of ARDS. The studies proposed in this grant are designed to determine: 1) if pulmonary gamma scintigraphy can accurately differentiate between cardiogenic pulmonary edema and permeability pulmonary edema associated with ARDS; and 2) in those patients with clinical evidence of ARDS if the magnitude and/or the duration of a positive "slope index" are associated with more severe ARDS and a worse prognosis or are affected by the etiology of ARDS. Should these questions be answered in the affirmative, this technique will be of value in the diagnosis of ARDS and objectively following its response to various therapeutic interventions.